Target volume definition for intensity-modulated radiotherapy after induction chemotherapy and patterns of treatment failure after sequential chemoradiotherapy in locoregionally advanced oropharyngeal squamous cell carcinoma.

AIMS: To validate our approach to target volume definition for intensity-modulated radiotherapy (IMRT) after induction chemotherapy and to analyse the pattern of treatment failure in patients with locoregionally advanced oropharyngeal squamous cell carcinoma (SCC) after sequential chemoradiotherapy (SCRT). MATERIALS AND METHODS: We studied all patients with locoregionally advanced oropharyngeal SCC treated with SCRT, definitive IMRT and no prior surgery between December 2004 and February 2010. SCRT consisted of three cycles of induction chemotherapy followed by IMRT with concurrent weekly chemotherapy. Our approach to IMRT tumour volume definition after induction chemotherapy was similar to recommendations from published clinical practice guidelines. Volumetric expansion was used to create the high-dose clinical target volume with a margin of 10 mm. The high-dose planning target volume (PTV) was treated to 65 Gy, whereas the prophylactic-dose PTV received 54 Gy over 30 fractions using the simultaneous integrated boost technique. The location and extent of each treatment failure was recorded, reconstructed on the planning computed tomography images and analysed using the dose distribution of the IMRT plan. RESULTS: Fifty-two patients were included. The median follow-up was 32.2 months (range 5.0-67.1 months). There were seven local failures, no regional recurrences and one with distant disease. None of the patients required post-treatment neck dissection. All local failures were in-field and occurred within the high-dose PTV. There were no marginal recurrences. Actuarial recurrence-free, disease-specific and overall survival rates at 3 years were 83.9, 85.9 and 79.7%, respectively. CONCLUSIONS: The absence of marginal recurrences validated the approach to IMRT target volume definition after induction chemotherapy proposed by clinical practice guidelines and practised at our institution. It suggested a lack of benefit with the use of larger geometric margins and additional anatomical expansion for the high-dose clinical target volume. SCRT resulted in excellent regional and distant disease control in patients with locoregionally advanced oropharyngeal SCC.